Goodwill and Intangible Assets (Summary of Intangible Assets) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 49,768	$ 48,470
Accumulated Amortization	(36,831)	(36,104)
Net Carrying Amount	12,937	12,366
Technology [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	29,090	27,882
Accumulated Amortization	(22,554)	(22,197)
Net Carrying Amount	$ 6,536	$ 5,685
Weighted Average Amortization Period	5 years 3 months 18 days	5 years 3 months 18 days
Customer relationships [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 15,984	$ 15,978
Accumulated Amortization	(10,788)	(10,457)
Net Carrying Amount	$ 5,196	$ 5,521
Weighted Average Amortization Period	8 years	8 years 18 days
Trade names [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 1,290	$ 1,289
Accumulated Amortization	(1,288)	(1,283)
Net Carrying Amount	$ 2	$ 6
Weighted Average Amortization Period	2 years 1 month	2 years 1 month 12 days
Non-compete agreements [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 1,440	$ 1,439
Accumulated Amortization	(1,440)	(1,439)
Net Carrying Amount	$ 0	$ 0
Weighted Average Amortization Period	2 years 3 months 12 days	2 years 3 months 12 days
Patents [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 1,702	$ 1,620
Accumulated Amortization	(526)	(493)
Net Carrying Amount	$ 1,176	$ 1,127
Weighted Average Amortization Period	13 years 2 months	13 years 1 month 18 days
Other [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 262	$ 262
Accumulated Amortization	(235)	(235)
Net Carrying Amount	$ 27	$ 27
Weighted Average Amortization Period	2 years 8 months 12 days	2 years 8 months 18 days